/** * ZTEST * * Returns the Weibull distribution. Use this distribution in reliability * analysis, such as calculating a device's mean time to failure. * * @param float $value * @param float $alpha Alpha Parameter * @param float $beta Beta Parameter * @param boolean $cumulative * @return float * */ public static function ZTEST($dataSet, $m0, $sigma = null) { $dataSet = PHPExcel_Calculation_Functions::flattenArrayIndexed($dataSet); $m0 = PHPExcel_Calculation_Functions::flattenSingleValue($m0); $sigma = PHPExcel_Calculation_Functions::flattenSingleValue($sigma); if (is_null($sigma)) { $sigma = self::STDEV($dataSet); } $n = count($dataSet); return 1 - self::NORMSDIST((self::AVERAGE($dataSet) - $m0) / ($sigma / SQRT($n))); }